Chasteuil and his partners spent their time in the quest for the philosopher's stone, contact with which was to convert metals into gold; and, like the majority of alchemists, they believed that it was to be found in the solidification of mercury. 'The hermetic philosophers,' writes M. Huysmans, 'discovered--and modern science to-day does not deny that they were right--that the metals are compound bodies of identical composition. Their varieties are due simply to the different proportions of the elements in combination; it is possible then, by the aid of an agent that would alter these proportions, to change these bodies one into another--to transmute mercury, for instance, into silver, and lead into gold. And this agent is the philosopher's stone, mercury: not ordinary mercury, which, to alchemists, is only a bastard metal' (M. Huysmans uses another expression), 'but the mercury of the philosophers, called also _lion vert_.' Among the papers of La Voisin was found an MS. poem in honour of the philosopher's stone: 'De l'or glorifié qui change en or ses frères.' The secret consisted in an elixir, of which a single drop, cast 'dans une mer profonde Où couleraient fondus tous les métaux du monde, Suffirait pour la teindre et fixer en soleil.'[7] Chasteuil and his fellows did not merely seek the solidification of mercury, which was to produce the philosopher's stone, but the liquefaction of gold by cold: this was to furnish a universal panacea. 'Liquid gold restores health and strength, gives flesh to greybeards and colour to the cheeks of girls, cures the plague,' and so on. Solid mercury being unobtainable, they sought, for the transmutation of metals, those powders or oils about which we hear so frequently at that period; and, as we shall see, they had the best reasons in the world for believing that they had put their finger on the secret, at least as far as silver[8] was concerned.